In the drilling of oil and gas wells, drilling rigs are used to create a well by drilling a borehole into the Earth's crust to reach oil and gas deposits. During the drilling process, as the depth of the borehole increases, so does the length and weight of the drill string. A drill string may include sections of drill pipe, a bottom hole assembly, and other tools for creating a well. The length of the drill string may be increased by adding additional sections of drill pipe as the depth of the borehole increases. Although a drill pipe section may come in any length, one common drill pipe section length is 30 feet.
A drilling mast or derrick may be used to support the weight of the drill string. The drilling mast or derrick may also accommodate additional sections of drill pipe as they are added to the drill string. To accommodate the weight of the drill string and to support the length of drill pipe that may be held above the ground, the mast or derrick may be strong and may be tall. The mast or derrick may also be heavy due to its strength and height.
While the drilling mast or derrick may support the weight of the drill string, the hoisting system, including drawworks, drilling line, and a pulley system, raises and lowers the drill string in and out of the borehole. The drawworks may include a rotating drum connected to a drive system. The drum may let out and reel in the drilling line that may pass through the pulley system. In the pulley system the drilling line threads through a crown block and traveling block (sometimes called a block and tackle) which increases the mechanical advantage of the system, and may allow the drawworks to move the drill string. The hoisting system may also be heavy due to the strength and power used to support and move the drill string.
A drilling rig may also include a substructure. The substructure may support the weight of the hoisting system and the mast or derrick and therefore may also be heavy. The substructure, like the hoisting system and mast or derrick, may be constructed of steel or other metal, may also distribute the weight of the drilling rig over a large area of the ground.
While some drilling rigs may be permanent structures that are erected and used at a single drilling site, some drilling rigs may be used to drill multiple wells. Drilling rigs that drill multiple wells may be transported from one drilling site to another.